Preparation And Synergistic Regulation Of Thermoelectric Performance Of N-Type SiGe Alloy Doped With Zn And Bi

As a representative of high-temperature thermoelectric（TE）materials,silicon-germanium（Si Ge）alloy has advantages such as structural stability,high temperature resistance,oxidation resistance,non-toxicity,and easy integration.By doping IIIA and VA elements,Si Ge alloy has excellent power factor and can provide uninterrupted power for high-power electronic devices.Therefore,Si Ge alloy has the potential for promotion and application in the TE field.However,the high thermal conductivity limits the improvement of the dimensionless thermoelectric figure of merit（z T）.Therefore,how to significantly reduce thermal conductivity without affecting power factor has become the core of Si Ge research field.In order to solve the above problems,in this paper,n-type Si Ge based TE materials were prepared using ball milling（BM）and spark plasma sintering（SPS）processes.Metals（Zn,Bi）were used as composite dopants to optimize TE properties,and combined with phase composition,microstructure and other characterization,the internal mechanism was deeply analyzed.The following are the main contents of this work:（1）Si Ge alloy was prepared by ball milling combined with SPS process.By optimizing the ball-to-powder ratio and ball milling time,it was found that when the ball-to-powder ratio was 40:1 and the ball milling time was 25 hours,Si and Ge could form solid solution alloy completely.On this basis,n-type Si₈₀Ge₂₀P_x（x=0.5,1,2）and Si₉₀Ge₁₀P_x（x=1,1.5,2）bulk materials were prepared using SPS.The results indicate that as the P content increases,both electrical conductivity and thermal conductivity increase,while the Seebeck coefficient is the opposite.In addition,increasing Ge content can reduce thermal conductivity but also worsen power factor to a certain extent.Finally,at 873 K,the z T values of samples Si₈₀Ge₂₀P₁ and Si₉₀Ge₁₀P₂ reached 1.0 and 0.96,respectively.In the range of 323-873 K,the average z T values(z T_avg)reached 0.54 and 0.49,respectively,which are higher than those of traditional radioisotope thermoelectric generator（RTG）samples.（2）The doping of Zn element and regulating of sintering parameters together control the microstructure of Si₉₀Ge₁₀P₂ bulk material,improving its TE performance.On the basis of the optimized sample Si₉₀Ge₁₀P₂ in the first step,Si₉₀Ge₁₀P₂Zn_x（x=0.1,0.3,0.5）nanocomposites were prepared by doping Zn elements.By adjusting the content of Zn and sintering time,the Seebeck coefficient and electrical conductivity are synergistically optimized.While maintaining the power factor,the Zn precipitates,nano-pores generated by Zn evaporation,and the layered structures enhance the scattering of phonons,reducing the thermal conductivity to 2.59 W m^-1 K^-1.Finally,at 873 K,the z T value reached 1.23 and in the temperature range of 323-873 K,z T_avg reaches 0.6.Compared to traditional RTG samples,under the condition of only using half of the Ge content,the peak z T and z T_avg were increased by 50%and 30%,respectively,which has good application value.（3）Preparation of Si₈₀Ge₂₀P₁Bi_x（x=0.1,0.3,0.5）nanocomposites by doping Bi elements,and synergistic optimization of electroacoustic transport characteristics.On the basis of the optimized sample Si₈₀Ge₂₀P₁ in the first step,by adjusting the Bi content and optimizing the carrier concentration and mobility,the Seebeck coefficient was increased while the electrical conductivity only slightly decreased.Therefore,the power factor was optimized,which increased by about 5%compared to the pristine sample.Meanwhile,the scattering of phonons by microdefects such as Bi nanoparticles and twin boundaries results in a decrease in thermal conductivity to 2.26 W m^-1 K^-1.Finally,at 873 K,the z T value reached 1.3 and in the temperature range of 323-873 K,z T_avgreaches 0.69.Compared to traditional RTG samples,the peak values of z T and z T_avg increased by 59%and 50%respectively,further expanding the application prospects of Si Ge alloys in the medium to high temperature region.